In the past, microgravity protein crystal growth experiments utilizing a well known vapor diffusion method for concentrating a drop of protein solution within which protein crystals are grown have typically taken place in an apparatus housing a number of crystal growth experiments which are activated simultaneously. In one particular embodiment of such apparatus, crystal growth chambers are each provided with a wicking element dampened with a precipitate solution of a concentration calculated to draw solvent from the drop at a selected rate over a predetermined period of time, slowly concentrating the protein solution and allowing highly ordered protein crystals to form. The protein droplet is situated at the end of a single pipette or side-by-side pipettes located near the wicking element, with the pipettes each coupled to a small syringe containing, in the single pipette version, a pre-mixed solution of precipitate and protein solution. When deployed, the pre-mixed solution forms a drop at the end of the pipette. Each pipette of the side-by-side version is coupled to a separate syringe, one containing the protein solution and the other containing a precipitate solution, with mixing of the solutions occurring upon deployment. This mixing may be achieved by repeatedly cycling the two fluids into and out of the pipettes and syringes, or by simply allowing the fluids to mix by diffusion after the drop is deployed. The syringes are filled prior to flight, and the pipettes capped to prevent fluid loss by plugs connected to a common operating mechanism. When the operating mechanism is operated, all pipettes are uncapped simultaneously. Likewise, plungers of the syringes are also coupled to a common operating mechanism so that when operated, the drops are deployed simultaneously.
While this type device has been proven to work relatively well during several Space Shuttle flights, problems have occurred. Most notable among these problems is the difficulty of achieving complete mixing, especially when dissimilar fluids are mixed. Another problem is that the mechanism that deploys the drops is not designed for repeated cycling, and possibly may fail. Additionally, in some instances, the drops were lost due to the relative instabilities between the drops and pipettes during maneuvers in space. Further, cycling of the fluids as described introduces air bubbles therein, and the mechanical action introduces small but unacceptable temperature rises in the crystal growth enclosure, which is temperature-regulated to .+-.0.1 degree C. Still further, as the syringes are constructed of polysulfone, a translucent material, the solutions are difficult to load and evaluate, and the capping procedure cannot be evaluated for its sealing and compatibility before flight. Further yet, large crystals may not be collectible, and marginally collectible crystals may become damaged as they are drawn back into the small openings of the pipettes, or otherwise become "hung" on a surface between the two pipettes.
Accordingly, it is an object of this invention to provide an improved crystal growth apparatus that more efficiently mixes precipitate and protein solutions, is better configured to support a drop of solution, and can capture and protect crystals of the largest size grown.